As compared with a traditional liquid crystal panel, an active matrix/organic light-emitting diode (AMOLED) panel has such features as rapid response, high contrast and wide viewing angle, so there is a growing concern about AMOLED for display technology developers.
The AMOLED is driven by a pixel circuit to emit light. An existing 2T1C sub-pixel 10 consists of two thin film transistors (TFTs) and one capacitor (C), i.e., a driving TFT DTFT, a switch TFT T1 and a storage capacitor Cst as shown in FIG. 1. The switch TFT T1 is controlled by a scanning signal Vscan so as to control the input of a data voltage Vdata, the driving TFT DTFT is configured to control an OLED to emit light, and the storage capacitor C is configured to apply a maintaining voltage to a gate electrode of the driving TFT DTFT.
FIG. 2 is a driving sequence diagram of the 2T1C sub-pixel 10 in FIG. 1. A working procedure of the 2T1C sub-pixel 10 may be described as follows. When the scanning signal Vscan is at a high level, the switch TFT T1 is switched on, and the storage capacitor Cst is charged by a gray scale voltage Vdata on a data line. Meanwhile, the data voltage Vdata is applied to the gate electrode of the driving TFT DTFT, and the driving TFT DTFT is driven by a driving voltage ELVDD for the pixel circuit so as to operate in a saturation state, thereby to drive the OLED to emit light. When the scanning signal Vscan is at a low level, the switch TFT T1 is switched off, the maintaining voltage is applied by the storage capacitor Cst to the gate electrode of the driving TFT DTFT, and the driving TFT DTFT is driven by the driving voltage ELVDD so as to still operate in the saturation state, thereby to enable the OLED to emit light continuously. In the prior art, in order to ensure the driving TFT DTFT to operate in a saturation region and emit light normally, usually a relatively high driving voltage ELVDD is applied to a source electrode of the driving TFT DTFT of the OLED pixel circuit, and a value of the driving voltage remains unchanged, i.e., the OLED is driven at a constant voltage. However, at certain timings, e.g., when the data voltage is very low and a high driving voltage is not required, a power loss will take place and a temperature of an element will increase if a high voltage is applied. Hence, an existing method for adjusting the driving voltage for the 2T1C sub-pixel 10 may cause a great dynamic loss and a large temperature rise.